Described herein are peptide analogs of glucagon-like peptide 1 (GLP-1) that retain agonist activity, but are more resistant to proteolytic degradation than native GLP-1. In the analogs, at least one α-amino acid found in the native GLP-1 is replaced with a β-amino acid residue, which may or may not be cyclically constrained. Pharmaceutical compositions containing the analogs are described, as are methods to treat diabetes, and methods to make proteolytically resistant GLP-1 analogs.